Trays in which multiple fans are arranged in a kind of drawer are known, for cooling in telephone and broadcast facilities. Such arrangements make it easy to replace defective fans, but require a great deal of space that is not available in many applications. Such trays are also heavy, which is undesirable for mobile applications, since it increases energy consumption.
In motor vehicles, a single radial blower that has a corresponding size in all three spatial directions is usually used for ventilation. In small cars, especially, it can be difficult to find an installation space for it. This is true in particular for hybrid vehicles with their large and heavy batteries, which can become very hot during operation and must then be efficiently cooled.